"Lothar" <les### [at] helixnihgov> wrote:
> Hi Dr. Ricky,
>
>    adding the keyword hollow definitely changes something. It seems to
> over-compensate now. The white fog in the back seems to be greatly enhanced!

I've been playing around with this scene some more (even making my *own*
different test scene), and YES, the hollow keyword makes the fog re-appear
behind the triangle. The 'over-compensation' of the fog was really difficult to
track down, but I think I've solved that too: It's a strange combination of the
position of your two light sources (probably the one at <0,0,100>) -- and the
addition of specular and roughness to your triangle. Comment specular and
roughness out and the 'extra' fog effect disappears! Or move the lights to some
odd angles relative to the triangle.

Your triangle does have an 'inside' on its back face (and it extends
into infinity!) It's not a 'closed' shape, like a box or sphere. So the
'missing' fog is 'inside' it (as far as the camera sees.) Hollow does fix that.

HOWEVER...
Even though the fog documentation does mention the use of hollow, it's not in
this context. It says that the CAMERA cannot be inside a 'non-hollow object.' It
doesn't say that the fog itself is not seen there regardless of the camera
location. Take a look here (in the v3.62 included documentation)...

2.3.5.3.7  Fog and Hollow Objects

That explanation probably assumes that any objects in the fog are closed
ones, not like an 'open' triangle shape. But some clarification there would be
helpful!

Post a reply to this message